Typically, snowmobiles include two skis at the front for turning the vehicle, each ski being connected to the vehicle through a suspension assembly.
Different type of skis have been used in the prior art but one of the most popular type of skis currently used are “single-keel skis”. A “single-keel ski” is a ski that incorporates a single keel projecting from the ground engaging surface of the ski, the keel has a single or double runner(s), usually made of carbon steel with carbide inserts or other suitable hard materials, which run(s) longitudinally along part of the length of the underside of the keel for contacting the ground whenever the snowmobile is driven on hard surfaces.
The ski stance for snowmobiles is determined as the distance (or width) between the two skis. In particular, where a snowmobile is provided with a pair of single-runner skis, which is the more typical example, the ski stance is measured as the distance (or width) between the runners at the bottoms of each ski.
The stability of a snowmobile is affected by at least the two following factors: (i) the ski stance, and (ii) the location of the intersection point between the steering axis of each ski and the ground relative to the point of contact between the ski's runner and the ground. Regarding the first factor, it has been determined that increasing the ski stance directly increases the lateral distance between the center of gravity of the vehicle and the point of contact of the runners on the ground, the runners bearing at least the weight of the front portion of the vehicle. The further the weight-bearing points of the front portion of the vehicle, i.e. the runners, are from the center of gravity of the vehicle, the better will be the stability of the vehicle, even more so when the vehicle is turning, which is described as an improved “turning stability”.
On the other hand, it has been determined that the second factor identified above more significantly affects the stability of the vehicle when it is driven in straight line, which is known as the “straight-line stability”. When the runner of each ski does not have a contact point with the ground which coincides with the intersection point between the steering axis of the corresponding ski and the ground, the friction between the runner and the ground creates a moment about the steering axis of the ski.
It is currently difficult to simultaneously improve both the turning and the straight-line stability of a snowmobile. Since the distance between the two skis of a snowmobile is limited in various jurisdictions, generally to forty-height (48) inches, the most common way to improve turning stability is to increase ski stance by moving the keel and runner toward the exterior side of the ground engaging surface of each ski. However, since the steering axis of the ski is very often vertical and generally aligned with the center of the ski, widening the ski stance through such displacement of the keel and runner results in the steering axis and the runner not reaching the ground at a common point, and therefore disadvantageously affect the snowmobile's straight-line stability.
U.S. Pat. No. 6,860,352 to Mallette et al. teaches a system using a spindle (the element of the suspension and ski assembly that connects the one or more suspension arms with the ski and defines the steering axis) that facilitates altering the stance of a snowmobile without having to significantly rework or replace the snowmobile's suspension. However, Mallette et al. does not teach a way to align the steering axis such that it reaches the ground at a common point with the runner
U.S. Pat. No. 5,038,882 to Zulawski teaches a way to improve straight-line stability by a particular alignment of the front suspension spindles and skis which induces “toe-out” of the skis, but this has no effect on the turning stability of the snowmobile and the keel is still disposed near the centerline of the ski.
U.S. Pat. No. 6,942,050 to Honkala et al. teaches a snowmobile front suspension assembly with a particular disposition of the spindles and suspension arms that improve maneuverability of the snowmobile when obstacles are encountered, but this has no direct effect on neither straight-line or turning stability of the snowmobile.
In view of the foregoing, there is a need for a front suspension and ski assembly design that would reconcile both improved turning and straight-line stability while respecting the various regulations limiting the total width of a snowmobile and therefore the maximum distance between the skis.